The Lewis (Le) blood group antigens, a and b, were originally defined by two anti-sera designated anti-Le.sup.a and anti-Le.sup.b. See Andersen (1948), Acta Path. Microbiol. Scand. 25: 728; Mourant, (1946) Nature 158: 237. Based on these anti-sera, four Lewis phenotypes were distinguished: Le.sup.a+b+, Le.sup.a-b-, Le.sup.a+b-, and Le.sup.a-b+. An individual, therefore, may possess one Lewis antigen (Le.sup.a+b- or Le.sup.a-b+), both Lewis antigens (Le.sup.a+b+), or neither Lewis antigen (Le.sup.a-b-). See generally, R. Race and R. Sanger, Blood Groups In Man Chp. 9 (6th ed. 1975).
Le.sup.a and Le.sup.b antigens occur as a terminal sugar sequence of glycolipids and glycoproteins in human saliva, serum, erythrocytes and other body fluids and tissues. The Le.sup.a antigen contains the terminal sugar sequence: ##STR1## and the Le.sup.b antigen contains the terminal sequence: ##STR2## The Le.sup.b antigen, as can be seen, contains the same terminal sequence as the Le.sup.a antigen with the adition of a fucosyl residue.
It is important to screen for Lewis blood group phenotypes prior to blood transfusions. If the donor's Lewis phenotype does not match the receipent's, a haemolytic transfusion reaction can result.
The Lewis blood group antigens are also related to the gastrointestinal cancer-associated antigen (GICA), which is present on cells of adenocarcinoma of the colon, stomach, or pancreas. GICA's antigenic terminal is sialylated lacto-N-fucopentaose II, which is a sialylased Le.sup.a antigen. It is believed that an individual must be able to synthesize the Lewis terminal sugar sequences in order to express GICA, the same enzymes being involved. See, e.g., Koprowski et al., Lancet, June 12, 1982, at 1332-1333. It is desirable, therefore, to know whether an individual is Le.sup.a-b- (approximately 5% of the population) if a diagonistic assay for the presence of GICA is negative.
Assays for Lewis phenotypes employ anti-sera obtained from humans or animals. Several problems exist with anti-sera. First, anti-sera are by necessity polyclonal in nature. Most anti-Le.sup.a sera contain some weak anti-Le.sup.b when obtained from Le.sup.a-b- donors. Precipitating and agglutinating anti-Le.sup.a sera has been obtained from animals, such as, chickens, rabbits and goats. Anti-Le.sup.b sera often contains anti-H antibodies which can result in a false indication of Le.sup.b+. The H antigen is a precursor of the Lewis antigens. See R. Race and R. Sanger, supra, 338-39.
Murine hybridomas have been reported that produce monoclonal antibodies directed against the Le.sup.b antigen. Brockhaus et al., (1981) J. Biol. Chem. 256: 13223. Some of these monoclonal antibodies, however, have been found to exhibit cross-specificity with the H blood antigen.
It would be desirable, therefore, to develop an assay that employs monoclonal antibodies that selectively bind either the Le.sup.a antigen or the Le.sup.b antigen, but not both. Furthermore, it would be desirable to employ monoclonal antibodies that do not cross-type for other blood group antigens.